1. Field of the Invention
The present invention relates to a polishing machine of polishing a workpiece with a slurry, a workpiece supporting table pad, and a polishing method. Specifically, the present invention relates to a polishing machine including a machine for temporarily placing and holding a pre-polished or post-polished workpiece on a workpiece supporting table; a workpiece supporting table pad; and a polishing method.
The present invention also relates to a manufacturing method of a semiconductor device which is manufactured using CMP (chemical mechanical polishing) and a polishing machine suitable for CMP used for manufacturing a semiconductor device and, more particularly to a manufacturing method of a semiconductor device and a polishing machine whereby an abrasive adhered to a polished surface is cleaned quickly.
2. Description of the Prior Art
(First Prior Art)
In recent years, as semiconductor devices have been increasingly miniaturized, surfaces of wafers (semiconductor substrates) on which insulating films and conductor films are formed are required to be smoothed with precision. In order to meet the needs, chemical mechanical polishing (CMP) machines are widely used nowadays. CMP machines are used in various processes for manufacturing semiconductor devices, such as polishing silicon wafers which are going to be turned into substrates, forming interconnects by use of the damascene method, and smoothing insulating films. In addition, CMP machines are used for manufacturing hard discs (magnetic recorders), manufacturing multichip modules (MCMs: hybrid integrated circuits), polishing lenses, and doing the like.
FIG. 1 is a schematic diagram showing an outline of a CMP machine used for manufacturing semiconductor devices. As shown in FIG. 1, the CMP machine includes a platen (table) 10, a polishing head (polishing carrier) 14, a slurry supplying nozzle 15 and a conditioning disc 12.
An abrasive pad (abrasive cloth) 11 is mounted on the platen 10. This platen 10 is fixed to a rotary shaft 10a, and rotates in response to rotation of the rotary shaft 10a. The polishing head 14 is disposed above the platen 10. A member for adsorbing and holding a wafer 13 is provided to the underside of this polishing head 14, and this member is termed as a membrane. The polishing head 14 is fixed to a rotary shaft 14a, and rotates in response to rotation of the rotary shaft 14a. 
A conditioning disc 12 is also disposed above the platen 10. This conditioning disc 12 is fixed to a rotary shaft 12a, and rotates in response to rotation of the rotary shaft 12a. This conditioning disc 12 is used for keeping the surface of the abrasive pad 11 in a condition optimal for polishing the wafer during and after the polish. The conditioning disc 12 is also termed as a conditioner, and as a dresser.
The slurry supplying nozzle 15 is connected to a slurry supplying machine (not illustrated) through a tube 15a. A slurry is dropped from the slurry supplying nozzle 15 to the abrasive pad 11. A slurry dropped to the top of the abrasive pad 11 is supplied to the interstice between the abrasive pad 11 and the wafer 13 by means of rotation of the platen 10. Furthermore, a surface of the wafer 13 is mechanically and chemically polished with an abrasive (abrasive grains) and a chemical fluid contained in the slurry and the abrasive pad 11.
FIG. 2 is a perspective view of the CMP machine. FIG. 3 is a diagram showing a cross-section view of a load cup (also termed as a load/unload station or an HCLU) of the CMP machine and a partial cross-section view of the polishing head of the CMP machine. Detailed descriptions will be provided for the CMP machine by use of these figures.
As shown In FIG. 2, generally-used CMP machines are provided with a plurality of platens 10 (three platens 10 in the figure) and a load cup 20 on a base 2. A slurry supplying arm 31 provided with slurry nozzles at the end of the slurry supplying arm 31 and a conditioning disc driving arm 32 to which a conditioning disc 12 is attached are arranged around each of the platens 10. In addition, the polishing head 14 is attached to a head unit 30 supported by a rotary shaft 30a. In the case of the CMP machine shown in FIG. 2, three platens 10 and one load cup 20 are arranged around the rotary shaft 30a. The head unit 30 is provided with four polishing heads 14 corresponding to the three platens 10 and the lord cup 20. Wafers are transferred to the tops of the respective platens 10 by means of causing the head unit 30 to rotate while the wafers are adsorbed and held by the polishing head 14. Incidentally, the rotary shafts 14a of the polishing heads 14 are designed to reciprocate in the direction of a radius in which the head unit 30 rotates as shown by arrows in FIG. 2.
As shown in FIG. 3, the inside the load cup 20 is provided with a pedestal (workpiece supporting table) 21 for temporarily holding the wafers 13 (workpieces) which are going to be polished, or which have been polished. The inside of this pedestal 21 is a hollow, and the top of the pedestal 21 is provided with a plurality of nozzles (holes) 21a connecting with the hollow. The unfilled space (hollow) inside the pedestal 21 is connected with an internal unfilled space inside a hollowed shaft 22 supporting the pedestal 21. This internal unfilled space of the shaft 22 is connected to a source of supply of nitrogen gas, a source of supply of pure water and a vacuum pump through a plurality of selector valves (not illustrated).
Furthermore, the inside of the load cup 20 is provided with a positioning member (not illustrated) for aligning the wafers 13 respectively to the polishing heads 14. Incidentally, in the case of the CMP machine shown in FIGS. 2 and 3, the periphery of the pedestal 21 is provided with nozzles 23 for ejecting pure water to the polishing heads 14. These nozzles 23 are connected to the source of supply of pure water through piping 24.
The bottom of each of the polishing heads 14 is provided with an adsorbing member including a membrane 16 made of a thin film of rubber. This adsorbing member is connected to an air pressure regulating system. When the inner unfilled space of the adsorbing member is placed under a negative pressure, the membrane 16 is depressed upwards, and thus adsorbs the wafer 13. Such a configuration of CMP machines has been known heretofore (see Japanese Patent Laid-open Official Gazette Nos. 2003-71709 and Hei. 9-174420, and Japanese Patent Official Gazette No. 3439970, for example).
It should be noted that, as shown in a side view of FIG. 4A, a pedestal pad 25 is arranged on the pedestal 21 for the purpose of preventing the surface of the wafer 13 from being scratched. This pedestal pad 25 is made of a soft material. Specifically, the pedestal pad 25 is a two-layered configuration, where the upper layer is a vertical foam made of polyurethane, and the lower layer is a layer obtained by impregnating a non-woven fabric made of polyurethane fibers with polyurethane resin. Moreover, as shown in a plan view of FIG. 4B, the pedestal pad 25 is provided with holes 25a at positions matching with the nozzles 21a provided to the pedestal 21.
Incidentally, it is known that copper to be used for interconnects is prevented from being oxidized and corroded by means of keeping wafers, which have been polished by CMP, in an aqueous solution of benzotriazole (BTZ) (see Japanese Patent Laid-open Official Gazette No. 2000-277470, for example).
Generally, aluminum is used as a material for interconnects of semiconductor devices. However, in the case of highly-integrated and highly-performing semiconductor devices, copper is more used as the material for interconnects than aluminum, since copper has a smaller resistivity than aluminum and copper less causes electro-migration than aluminum. Chemical reaction makes greater contribution in a case where copper is polished by CMP than in a case when insulating films are polished by CMP. Incidentally, copper is more likely to be oxidized and corroded. In addition, the surface of copper which has been polished by CMP is extremely active, and oxidation and corrosion easily occurs in the surface. For this reason precautions are necessary for not only selection of a slurry and a cleaning fluid, but also treatment of wafers which have been polished.
However, in the case of conventional CMP machines, copper is likely to be oxidized and corroded from a time of completion of the polish until a time of the unloading (wafers are transferred out of the polishing machines). For this reason, further ingenuity has been required.
(Second Prior Art)
CMP is widely used, in a manufacturing process of a semiconductor device, for example, for planarization of an interlayer dielectric film, formation of embedded wiring and the like. As a polishing machine for performing CMP, a dry-in/dry-out polishing machine which combines a polishing unit having a platen and a cleaning unit for performing cleaning after polishing has been used recently. Hereinafter, a description is given for a conventional polishing machine which combines a polishing unit and a cleaning unit.
FIG. 5 is a plan view of a conventional polishing machine, showing a substantial configuration of a polishing machine which combines a polishing unit and a cleaning unit. A polishing machine 300, the whole of which is accommodated in a clean room 301, includes a carry-in/carry-out unit 310 for carrying a wafer in the clean room 301 or carrying out of the clean room 301, a polishing unit 320 for polishing the wafer by CMP, and a cleaning unit 340 for cleaning the wafer. The units are separated from each other so that an airflow between the units will be less in order to maintain a clean atmosphere in each unit.
On the carry-in/carry-out unit 310, a cassette 314 for accommodating the wafer before and after polishing is mounted. A robot arm 311 is also provided for taking the wafer out of the cassette 314 or accommodating the wafer in the cassette 314.
The polishing unit 320 has two platens 321 and 322, and a turntable 325 is provided therebetween. An abrasive pad is attached to the top surface of the platens 321 and 322 so as to supply slurry. Also, two polishing heads 323, 324 are provided for each of the platens 321 and 322, and the wafer held on the bottom of the heads 323 and 324, is polished by being pressed against the abrasive pad. The heads 323 and 324 are movable vertically relative to the sheet of FIG. 5.
A turntable 125, which has four placing tables 326 on the top surface thereof, is turned to carry a wafer placed on a placing table 326. Furthermore, the wafer placed on the placing table 326 can be cleaned with a cleaning fluid.
In addition, between the turntable 325 and the platen 321, and between the turntable 325 and the platen 322, cleaning stages 327 and 328 for cleaning the wafer are provided respectively. The cleaning stages 327 and 328 rotatingly travel from the position shown in FIG. 5 to the position of the placing table 326 and can carry the wafer between the positions.
The cleaning unit 340 includes two cleaners 342 and 343, stages 341 and 345 for carrying-in and for carrying-out, a drier 344, and a robot arm 346 for carrying a wafer rotatingly.
The wafer is taken out of the cassette 314 by the robot arm 311, and then placed on a thicknessmeter 313 as a point of delivery. The wafer placed on the thicknessmeter 313 is carried in the polishing unit 320 by the robot arm 312, and then placed on the placing table 326 provided in the polishing unit 320.
The wafer placed on the placing table 326 is adsorbed on the bottom of either of the heads 323 or 324, carried to the top surface of the platens 321 and 322 by the travel of the heads 323 and 324. The wafer is then pressed against the abrasive pad on the top surface of the platens 321 and 322 at that position, and then polished.
The polished wafer is carried to the cleaning stage 328 by the travel of the heads 323 and 324, cleaned there, and then placed on the placing table 326.
Next, after carrying the wafer placed on the placing table 326 to the thicknessmeter 313 followed by measuring its thickness, the robot arm 312 places the wafer on the placing table 326 again. Then, using the platen different from the one used for the previous polishing, the wafer is finish-polished and brought back to the placing table 326 through the cleaning stage.
The finish-polished wafer is placed on the stage 341 in the cleaning unit 340 by the robot arm 312. After being carried to the drier 344 through the cleaner 342 for main cleaning and the cleaner 343 for finish cleaning and then dried, the finish-polished wafer is placed on the stage 345 by the robot arm 346.
The wafer placed on the stage 345 is accommodated by the robot arm 311 again in the cassette 314 for accommodating the wafer. Thus, the polishing machine, in which all the polishing steps are automatically taken, can achieve a dry-in/dry-out process without manual operations during the process. Consequently, all the polishing steps including polishing and cleaning can be taken at a highly clean atmosphere, thereby obtaining an excellent polished surface with fewer defects (for example, see PC (WO) No. 2005-523579).
The inventors of the present application, however, think that the above described conventional polishing machine has the following problems. Specifically, the conventional polishing machine carries the polished wafer to the placing table or cleaning stage and then cleans the polished surface of the wafer. Consequently, there is time for a few seconds from the end of polishing until the clean of the polished surface, when the polished surface, in a state that slurry remains adhered to the polished surface, is exposed to an atmosphere. As a result, the wiring appearing on the polished surface, particularly copper wiring, corrodes and consequently, the quality of the semiconductor device to be manufactured is deteriorated.
The experiments conducted by the inventors of the present invention clarifies that slurry is left even on the polished surface immediately after the so-called water polishing; consequently the surface of the copper wiring corrodes if exposed to an atmosphere; and the corrosion proceeds within 1-2 sec. It is from when the head holding the wafer on its bottom rises thereby separating the wafer from the abrasive pad until when the wafer starts being cleaned on the cleaning stage that the polished surface is exposed to an atmosphere immediately after polishing. Therefore, in order to suppress the corrosion of the copper wiring appearing on the polished surface, the wafer has to be cleaned before carrying to the cleaning stage after polishing.
It has been known that an improved polishing machine which prevents the corrosion on the surface of a compound semiconductor appearing as a polished surface by a polishing fluid, by cleaning the wafer quickly immediately after polishing (for example, see JP H07-201786A).
FIGS. 6A and 6B are figures for illustrating an operation of the conventional improved polishing machine, indicating a method of quickly cleaning the wafer immediately after polishing by cross-sectional views of the polishing machine. It should be noted that FIGS. 6A and 6B show a state immediately after polishing and a state when the head rises.
Referring to FIG. 6A, in this improved polishing machine, a wafer 364 held on the bottom of a polishing head 365 is polished by pressing against an abrasive pad 382 attached to the top surface of a platen 381. Immediately before the end of polishing, the wafer 364 travels to a prescribed position close to a periphery of the platen 381. Outside the platen 381, close to the prescribed position, a nozzle 376 for spraying a cleaning fluid 376b is provided.
Referring to FIG. 6B, the head 365 rises simultaneously with the end of polishing, the wafer 364 is held at a cleaning position above the platen 381 with a polished surface 364a downward. Next, the cleaning fluid 376b is sprayed from the nozzle 376 on the polished surface 364a of the wafer 364 so as to clean the polished surface 364a. The polishing machine, which starts cleaning the wafer 364 at a time of raising the head 365, can suppress the corrosion of the polished surface 364a drastically compared with a polishing machine which cleans the wafer 364 by carrying to a cleaning stage. It should be noted that a cleaning fluid 363a is supplied on the top surface of the abrasive pad 382 from the shower 363 immediately after raising the head 365 so as to clean the abrasive pad 382.
Also in the improved polishing machine, however, during the period from when the wafer 364 is separated from the abrasive pad 382 by the rise of the head 365 until when held at the cleaning position, since the polished surface 364a of the wafer 364 is exposed to an atmosphere, the corrosion proceeds on the polished surface 364a. Since the corrosion of the copper wiring proceeds rapidly in particular, unignorable corrosion occurs even during a time of raising the head 365 and consequently, the semiconductor device becomes less reliable.
It should be noted that the corrosion occurring during a time of carrying the wafer 364 from the abrasive pad 382 to a cleaning stage (for example, cleaning stages 327 and 328 shown in FIG. 5) in the abovementioned normal polishing process. The corrosion is corrosion on the surface layer of the copper wiring, and is corrosion enough to discolor the surface of the copper wiring. At the same time, serious corrosion enough to corrode the entire copper wiring (all the layers) occurs in case of trouble.
FIG. 7 is a sequence of the conventional polishing machine in case of trouble, and shows a sequence of the main operations of the polishing machine prearranged for time of trouble. Referring to FIG. 7, the conventional polishing machine is designed, when an occurrence of a trouble is detected, to stop its operation and wait for an operator's decision after taking the following (1)-(3) steps: (1) adsorbing the wafer to the head, raising from the abrasive pad, and suspending by holding; (2) stopping the rotation of the platen and head; and (3) stopping supplying slurry on the abrasive pad, supplying the cleaning fluid on the abrasive pad, and then rinsing the abrasive pad.
In such a sequence in case of trouble, during the period from when a trouble is detected and the head rises until when the operator makes a decision and reoperation, the polished surface of the wafer is exposed to an atmosphere with slurry remaining adhered thereto. Since it takes normally several minutes before the operator conducts the operation, the copper wiring to which slurry is adhered corrodes through all the layers thereof during this time. As a result, the trouble occurrence in the polishing machine causes a fatal defect in the semiconductor device, thereby decreasing the manufacturing yield of the semiconductor device drastically.
As described above, in the conventional CMP polishing machine (polishing machine for performing chemical mechanical polishing), when carrying the wafer from the platen to another apparatus, the wafer is firstly carried to an intermediate stage (for example, cleaning stage or placing table) and then cleaned on the intermediate stage. However, during a time of carrying the wafer from the platen to the intermediate stage, the wiring metal surface appearing on the polished surface of the wafer corrodes thereby deteriorating the reliability of the semiconductor device.
In the conventional improved CMP polishing machine which sprays a cleaning fluid from the nozzle on the polished surface of the wafer held above the platen after polishing so as to clean the polished surface, since the wafer can be cleaned before carrying to the intermediate stage, the corrosion can be greatly improved. However, by the time when the wafer is held at a cleaning position on the platen, specifically, during the period from when the wafer separates from the abrasive pad until rising up to the cleaning position, the metal wiring surface appearing on the polished surface corrodes and consequently, it is difficult to fully suppress the corrosion of the metal wiring appearing on the polished surface.
Furthermore, in the conventional CMP polishing machine, the machine stops in case of trouble, leaving the wafer held on the platen, and the wafer is left without cleaning. Consequently, there is a problem in that the wiring layer appearing on the polished surface corrodes through all the layers (from the surface to the bottom of the wiring layer). Since all the layers thus corroded cannot be recovered by the repolishing which removes only the surface layer, the manufacturing yield of the semiconductor device decreases.